1. Field of the Invention
This invention relates to a compression coupling for a service valve and more particularly to a coupling nut threadedly advanced into a fitting of a valve to wedge a gripping collar into frictional engagement with a conduit received in the fitting and apply a controlled compressive force upon a gasket seal around the conduit to effect a fluid tight connection of the conduit to the fitting.
2. Description of the Prior Art
It is the customary practice with the known plastic service valves to provide a valve body having flow passages that communicate with a valve seat and pipe stub ends that are connectable to a piping system. In one known arrangement, the pipe stub ends are butt or socket fusion joined to the pipes of the system which are fabricated of the same material as the valve. Another arrangement utilizes internally or externally threaded valve ends for connecting the threaded valve ends to matching piping by compression couplings.
Examples of known compression couplings that are adaptable for connecting valve pipe stub ends to transmission pipes are illustrated in U.S. Pat. Nos. 3,563,575; 3,865,410 and 4,008,911. For example, as disclosed in U.S. Pat. No. 3,563,575, a service line pipe is connected to a coupling body by the wedging action of a collar against an internal wedge surface of a nut threaded on the coupling body. The collar has an external wedge surface which is complementary to and cooperates with the internal wedge surface of the nut that surrounds the threaded end of the coupling and is threadedly connected to the coupling. An elastic deformable member, such as an O-ring or a gasket, encircles the pipe and is seated within a recess of the coupling. A thrust washer encircles the pipe between the adjacent ends of the nut and the coupling. As the nut is threaded onto the threaded end of the coupling, the internal wedge surface of the nut coacts with the external wedge surface of the collar to advance the collar into compressive relation with the washer against the end of the coupling and the O-ring.
One disadvantage of this type of compression coupling is premature seizing of the collar on the pipe before the nut is completely threaded on the coupling. This is encountered as a result of the wedging action of the nut on the collar where the nut and collar are wedged into gripping engagement and further axial advancement of the collar on the pipe is prevented.
Another recognized disadvantage of the known compression couplings is subjecting the sealing gasket to an excessive force applied by the collar due to over-torquing or uncontrolled rotation of the nut on the valve pipe stub end. If rotation of the nut is not controlled, the gasket may be compressed beyond its ability to maintain an effective seal around the pipe due to the excessive compression of the gasket by the collar as it is advanced upon rotation of the nut. Therefore, there is need in connecting a plastic service valve to service lines for a compression-type coupling that overcomes the above-recognized problems of both incomplete sealing of the gasket on the pipe and uncontrolled rotation of the nut on the valve pipe stub end to the point where the gasket is compressed beyond its ability to provide an effective seal.